Added article on JSHint freeze option

Author: James Allardice

option-articles/freeze-jshint.md

@@ -0,0 +1,77 @@
+<!---
+{
+    "titles": [
+        "freeze"
+    ],
+    "slugs": [
+        "option-jshint-freeze"
+    ],
+    "linters": [
+        "jshint"
+    ],
+    "author": "jallardice",
+    "subject": "option"
+}
+-->
+
+### What does this option do?
+
+The JSHint `freeze` option is used to disallow the extension of native object
+prototypes. This is often viewed as bad practice and was a relatively common
+source of bugs in older JavaScript environments. In the following example we
+attempt to add a method to reverse strings to the native `String` object:
+
+<!---
+{
+    "linter": "jshint"
+}
+-->
+```javascript
+/*jshint freeze: true */
+String.prototype.reverse = function () {
+    return this.split("").reverse().join("");
+};
+```
+
+The option does not prevent extension of native prototypes via the
+`Object.defineProperty` method since it allows you to safely extend such objects
+with non-enumerable properties:
+
+<!---
+{
+    "linter": "jshint"
+}
+-->
+```javascript
+/*jshint freeze: true */
+Object.defineProperty(String.prototype, "reverse", {
+    value: function () {
+        return this.split("").reverse().join("");
+    }
+});
+```
+
+*Side note*: the implementation of string reversal above is naive because it
+fails to take into account the way characters are encoded internally in
+JavaScript. See [this Stack Overflow answer][reverse] for a great explanation.
+
+### When should I use this option?
+
+The use of the `freeze` JSHint option will cause an "[Extending prototype of
+native object: '{a}'][native]" error, where "{a}" is the native prototype in
+question, any time it encounters an assignment that matches the rules discussed
+above. It's generally considered bad practice to extend native prototypes
+because it makes it easier to introduce bugs related to property enumeration and
+shadowing. See the article discussing the "[Extending prototype of native
+object: '{a}'][native]" error message for more details.
+
+Note that this is an *enforcing* option which means JSHint does not apply it by
+default. If you do not explicitly set this option to `true` JSHint will allow
+the extension of native prototypes anywhere in your code.
+
+#### Recommendation
+
+Set this option to `true` (disallows the extension of native prototypes).
+
+[reverse]: http://stackoverflow.com/questions/958908/how-do-you-reverse-a-string-in-place-in-javascript/16776621#16776621
+[native]: /extending-prototype-of-native-object